1. Field of Invention
The present invention generally relates to electrical surge protection devices, and more particularly to spark gaps formed on printed circuit boards.
2. Description of Prior Art
Broadband coaxial cable communications networks, such as CATV networks, include various types of electronic equipment mounted to outdoor utility poles. This electronic equipment is subjected to all types of weather conditions including, for example, lightening storms. Due to the importance of these communications networks to society, it is important that they be able to withstand the harsh conditions under which they operate.
On occasion, a high voltage surge may be transmitted through the coaxial cable to which the electronic components are interconnected, for instance, due to a lightning strike. If this high voltage surge is permitted to be picked up by the input or output pins of the interconnect device and transmitted to the electrical devices housed therein, the device would become inoperable due to the electrical components essentially melting or otherwise deteriorating as a consequence of the surge. A new connector would then need to be installed at the site of the surge.
In order to improve the reliability of the electronic components in a communications network, the interconnect units are generally equipped with some type of over-voltage surge protection device. IEEE Standard C62.41-1991 sets forth a recommended practice on surge voltages in low voltage power circuits. The surge protectors incorporated into the interconnect units may include, for instance, a single, conductive element positioned in adjacent, but spaced relation to the incoming signal. In the event of a transient, high voltage surge, the element will accumulate and discharge the over-voltage surge to ground prior to it passing through the electrical components. Incorporation of such surge protectors, however, add significantly to the complexity in manufacturing, and hence, the cost of an interconnect unit. In addition, if a voltage surge above what the protector is designed to handle is experienced by the connector unit, it will need to be replaced in any event.
3. Objects and Advantages
It is therefore a principal object and advantage of the present invention to provide an over-voltage surge protection device that is inexpensive to manufacture relative to the state of the art.
It is a further object and advantage of the present invention to provide an over-voltage surge protection device that can withstand multiple surges, hence increasing the life of the coaxial cable interconnect device.
Other objects and advantages of the present invention will in part be obvious, and in part appear hereinafter.
In accordance with the foregoing objects and advantages, the present invention provides an over-voltage surge protection device comprising a printed circuit board having a signal carrying conductive member having a plurality of nodes positioned therealong, and a conductive member running to ground also having a plurality of nodes positioned therealong. The nodes on the signal carrying member and ground member extend along a common path with corresponding ones of the signal carrying nodes positioned in adjacent, but spaced relation to the ground nodes. Preferably, the nodes are shaped in the form of triangles due to this particular geometry""s favorable ability to accumulate and discharge voltage.
The over-voltage surge protection device may be fabricated directly into the board without mounting any additional structure thereto. A circuit board substrate that contains a layer of conductive material coated thereon may be fabricated by removing conductive material (e.g., by laser ablation, chemical or photolithographic etching, or other conventional fabrication process) in all areas on the board other than the signal carrying members and the conductive member leading to ground. The area of non-conductive material separating the signal carrying members from the ground member become the spark gaps.
The spacing between the nodes (and their shape) determine the voltage level at which a spark will generate and shunt the circuit. The number of nodes present in the device will determine how many over-voltage surges it will be able to withstand.
In operation, as the relative voltage potential between two corresponding nodes approaches a predetermined value, a spark will generate across the gap that separates them. This spark discharges the voltage from the signal carrying member to the grounded member, thereby shunting the circuit. Any particular spark may cause a deterioration of the particular node which discharges the surge. However, due to the circuit board having a plurality of corresponding sets of nodes, it will be able to withstand at least an equal number of over-voltage surges.